1. Field of the Invention
The present invention relates to the concentration of incident radiation, such as visable solar energy and photophosphrescence, by use of internal Rayleigh-MIE scattering and optical wave guide devices.
2. Prior Art
Certain radiation energy can be utilized more efficiently when concentrated, for example solar energy radiation for power production or luminescence from photophosphorescence in markers and signs. The phenomenon of total reflection at the interface between material of different refractive indexes has been employed to concentrate radiation energy. The same principle is the basis of light propagation in dielectric wave guides commonly referred to as optical fibers. However, with respect to using dielectric wave guides for concentration of incident radiation energy, an important consequence of Snell's law of reflection between material of different refractive indexes is that a source of radiation incident of the wave guide core cannot contribute to guide modes within the wave guide. The incident radiation will reflect and refract at the wave guide boundaries, but none of the wave's energy will be trapped as a guided wave.
One method to overcome this problem is used by Zewail U.S. Pat. No. 4,227,939. Fluorescent dye in the wave guide core absorbs the incident radiation and by fluorescence emission scatters the energy within the core to permit photon capture in guide modes. The method requires a variety of fluorescent material to cover the solar spectrum due to the specific absorption wave lengths associated with each fluorescent dye.
The complication of this approach arises from the need to maximize the absorption of incident photons without creating unacceptable transmission losses in the wave guide modes. The device is a slab type dielectric wave guide in which the trapped photons are reflected repeatedly across the plates central axis and through various fluorescent absorbers. A fraction of the photon energy is dissipated during each fluorescent cascade event which causes a lossy collector.
In U.S. patent application Ser. No. 06/826,304 (U.S. Pat. No. 4,733,929) a coaxial diffuser is created within the core region of a circularly cylindric fiber by forming microspheres of air or other material of suitable refractive indexes in the wave guide core. The interface between the microspheres and the core material reflect and refract the incident radiation as the rays pass into diffuser and creates the internal scatter required to allow the incident radiation to enter guide modes. The use of prismatic shapes to create a difusser is a satisfactory method, however, certain material and manufacturing procedures favor the use of colloidal inclusions of material with a refractive index different from the core material to create a light scattering diffuser region in the wave guide.
A coaxial diffuser incident energy concentrator is a low gain low loss collector which will benefit by recycling the untrapped scattered radiation for rescattering and trapping in wave guide modes.